Adding new sub panel in garage with a wire too short

Question

A few years ago I had work done that included adding buried wires for a new sub panel in my detached garage. The wires were installed but were not long enough in the basement to reach my main panel. And, of course, they weren’t long enough in the garage, either. Is there a solution to this problem other than running new wires? The wires are the right size for the 100 amp sub panel just not long enough. They are about 20’ short in the basement and only 5’ too short in the garage. I want to add the sub panel to provide power for a level 2 EV charger and a 30 amp outlet for a camper. I wasn’t ready to do anything when the wires were installed but now it’s time. And my original contractor, when he saw the issue, didn’t charge me for that part of the work. Nice gesture but leaves me with a problem to be solved now.

Answer 1

Since it is a sub-panel and protected by a breaker in the main panel, two junction boxes and some wicked expensive Polaris connectors to join the actual wires inside the junction boxes will do the trick, along with more wire.

The junction boxes must be installed so that they are accessible, forever. No drywalling over them, etc. They have to be fairly large boxes for that size wire.

It's a much harder trick on a service entrance wire, since those are essentially unfused, or "fused at a level that permits lots of damage before it goes" anyway.